The present invention relates to a switching device for selectively switching a plurality of loads, a method of selectively switching a plurality of loads and a switching unit for use in the switching device and method.
It is a common requirement in many situations to conduct measurements of physical properties at locations remote from the site where such measurements are collated and actions taken. Examples include plant processes where, for example, the temperature, pH and pressures of various reactors need to be monitored; and security installations where many doors and windows need to be continually monitored to determine whether or not they are open or closed. In many of these situations, it is necessary to trigger a particular action to occur at a remote site depending on the values or status of the parameters being measured.
Apparatuses which detect the occurrence, position or value of an event, or which cause a particular action to be taken consist of three parts:
1. Transducer/transmitter. This is the component of the system which detects the parameter being measured, converts the information into a signal, such as an electrical signal, and transmits this signal to a central location for further processing.
2. Transmission medium. In many instances this is may be simply a single pair of electrical conductors. However, in some instances the transmission medium could be as complex as a signal coded into an electromagnetic carrier such as a radio signal or a light beam. In some specialized cases, such as areas with explosive mixtures of gases, the transmission medium may not be electrical and may be, for example, pneumatic, or, optical.
3. Receiver. This is the component of the system where the signal is received and processed. The value of the parameter being measured could be displayed or could initiate a particular action or both.
Many combinations of individual variants of these components can be put together to make a workable system to achieve the desired result.
At present, it is understood that any working system is a compromise between the complexity and cost of these three components. As a general principle, the simpler the transmission medium, the more complex will be the transmitter and receiver, and vice versa. For example, if there are 50 locations at which it is desired to record the temperature, to use a single pair of conductors as the transmission medium requires extensive coding/decoding at both ends. Alternatively, utilizing simple detectors and indicators, to monitor the same 50 locations would require 50+1 (common) conductors.
Thus it would be desirable to provide a device and a method whereby many transducers at remote sites could be monitored in a simple fashion via a minimal number of conductors. The same principle can also applied to cause desired actions to be effected at remote sites.